I gave a co-worker a ride home once and he was so impressed by my truck (it's not that impressive) that he and same friends chained two large cast iron weights to my hitch without my knowledge. I think the joke was that my truck had cast iron balls, they even painted them to match the truck. The first time I hit the brakes hard I heard this God-awful banging sound.
It was funny, but I drove I-90 everyday and the idea of one of those damn things coming loose at 80 mph and blowing a hole in someones car or person was too much.
They lasted a day, I agree it's a dumb trend, not the dumbest or toughest to explain thing you're likely to see in any given day but it's up there.